1) Field of the Invention
The present invention relates to rotatable cutting tools and, more specifically, to supporting one or more knives in alternate configurations.
2) Description of Related Art
Rotatable cutting tools are well known in the art and include, among others, saws, knives, cutterheads, heads or chucks with removable knives, drill bits, router bits, drills, end mills, moulders, and grinders of multiple shapes. These tools are used for cutting or grinding a variety of structural materials including, but not limited to, wood, metal, composite materials, plastic, foam, food products, and the like.
One conventional rotatable cutting tool, commonly referred to as a cutterhead, typically includes a generally cylindrical body that defines several longitudinally extending cavities for receiving knives. Each knife is inserted into one of the cavities and positioned so that a cutting edge of the knife extends from the cutterhead. The knife is then secured in place by tightening bolts that extend through part of the body and urge the knife against one wall of the cavity. Typically, the bolts are inserted through milled pockets on the outside of the cutterhead so that the heads of the bolts do not extend from the tool. The cutterhead is then rotated, for example, by a spindle that is connected to a motor. Structural material is brought into contact with the rotating knives, and the structural material is cut or scraped by the knives.
The configuration of the knives relative to the body affects the type of cutting or scraping that is achieved. For example, the hook and shear angles of the knives can affect the degree of material that is removed by each knife and the surface that is left on the structural material. The hook angle is measured as the angle between a leading surface of the knife and a radial line of the body that extends through the edge of the knife. A positive hook angle indicates that the leading surface of the knife is angled toward the direction in which the knife rotates. A knife with zero or little hook angle contacts the structural material so that the edge of the knife is approximately perpendicular to the surface of the structural material, thus resulting in a primarily scraping action of the structural material. A knife with positive hook angle, however, tends to achieve a slicing action because the cutting edge is directed closer to the direction of motion of the knife relative to the structural material.
The shear angle is measured as the angle between the longitudinal extension of the blade and the longitudinal axis of the body. For example, a zero shear angle indicates that the blade is parallel to the longitudinal axis of the body. A non-zero shear angle indicates that the blade is angled relative to the body so that a first end of the blade leads the blade and the opposite end of the blade trails as the body and blade are rotated.
An improper hook or shear angle can result in fracturing of the wood, rough or uneven work surfaces, excessive wear of the knives, and other poor cutting characteristics. The best hook and shear angle can depend on the structural material, including grain, fracture, and hardness characteristics. Thus, processing different structural materials can require adjustment of the hook and/or shear angle of the knives. For example, it is known in the art to use a hook angle of about 12° when cutting certain hard woods and 20° when cutting certain soft woods. Because the hook and shear angle of the knives is typically determined by the configuration of the cavities of the cutterhead, adjusting the hook or shear angle can require changing the knives and/or cutterhead, which can be time consuming, thereby reducing machine efficiency. Additionally, keeping multiple cutterheads with different hook and shear angles on hand for different processes requires a disadvantageous additional expense.
A known cutterhead includes a first pair of cavities configured at a first hook angle, and a second pair of cavities that are completely separate from the first pair of cavities and configured at a second hook angle. Knives are positioned in either the first or the second pair of cavities, and fillers are typically positioned in the other pair of cavities such that the fillers do not extend from the cavities. Bolts are used to secure the knives and fillers in the respective cavities. When it is desired to adjust the hook angle of the knives, the position of the knives and fillers are reversed. Thus, a single cutterhead provides two modes of operation, each characterized by a distinct hook angle. However, the provision of additional cavities that are not occupied by knives can change the rotational and balance characteristics of the cutterhead and the tool can be damaged if used without securing appropriate fillers in the cavities that are not being used to secure knives. If fillers are positioned in the unused cavities, there is a risk that improperly sized or weighted fillers will be used, thereby increasing the risk of tool failure and damage to nearby equipment. Additionally, the milled pockets provided for the bolts can also adversely affect the strength of the tool as well as the rotational and weight characteristics of the tool. Further, if the bolts are not properly tightened, the knives and/or fillers may become loose during operation and be projected from the tool.
Thus, there exists a need for an improved rotatable cutting tool that can support one or more knives in alternate angular configurations to achieve multiple hook angles at one or more shear angles. Preferably, the cutting tool should reduce the likelihood of incorrect installation of knives, fillers, bolts, and/or other components. Additionally, the cutting tool should be compatible with different knives and adaptable to conventional tool variations.